Our BSON library has bson.Marshal which will take interface{} and create a BSON document. We do not have a function like bson.MarshalValue to take interface{} and create an arbitrary BSON value (not necessarily a document). This is something that could be useful as part of an implementation for MarshalBSONValue for a struct type. See GODRIVER-1340 for a use case.

I wrote up a code sample to show a use of this and how it's handled now: https://gist.github.com/divjotarora/5bc3b6f85ef1030df6db83648c91dea6

CC craiggwilson may.hoque Craig mentioned that this could be useful for Data Lake (something about marshalling aggregation pipelines, which are arrays). Can you elaborate on the use case?